© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 910 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com COMMUNICATION Synthesis of Metal Nanoparticles Inside Living Human Cells Based on the Intracellular Formation Process Waleed A. El-Said, Hyeon-Yeol Cho, Cheol-Heon Yea, and Jeong-Woo Choi* Dr. W. A. El-Said, Prof. J. W. Choi Interdisciplinary program of Integrated Biotechnology Sogang University 35 Baekbeom-ro, Mapo-gu, Seoul 121–742, Republic of Korea E-mail: jwchoi@sogang.ac.kr H. Y. Cho, Dr. C. H. Yea, Prof. J. W. Choi Department of Chemical and Biomolecular Engineering Sogang University 35 Baekbeom-ro, Mapo-gu, Seoul, 121–742, Republic of Korea Dr. W. A. El-Said Department of Chemistry Faculty of Science Assiut University Assiut, 71516, Egypt Dr. C. H. Yea Research Institute for Basic Science Sogang University 35 Baekbeom-ro, Mapo-gu, Seoul, 121–742, Republic of Korea DOI: 10.1002/adma.201303699 Developing nanoparticles that target the cell’s nucleus is a promising approach in biological research because of the genetic information inside the nucleus. However, nuclear tar- geting is difficult to achieve because nanoparticles have to first pass into the cytoplasm and then cross the nuclear membrane. Here, the ability of the intracellular and extracellular forma- tion of metal nanoparticles based on the reduction of metal salts was investigated in different cell lines. Moreover, the cells were fixed by metal ion solution during the metal nanoparticle synthesis process. Atomic force microscopy (AFM), transmis- sion electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and UV-Vis absorption were utilized to identify the formation of metal nanoparticles inside the cells as well as in the incubation solu- tion. In addition, the potential of using these nanoparticles to enhance the Raman signals from the cell was examined. Synthesis of metallic nanoparticles (NPs) with different shapes and sizes is currently in high demand and is a chal- lenging issue in various fields including nanotechnology and nanobiotechnology, [1] due to their unique physicochemical and optoelectronic properties. [2] The unique properties of gold (Au) NPs compared to other metals NPs (chemical, physical, optical, easy preparation, efficient bioconjugation, potential noncytotoxicity, tunable, enhanced scattering and absorption properties, etc.), provide Au NPs great potential applications in several fields such as optoelectronic devices, ultrasensitive biochemical sensors, [3] medial therapeutics, [4] catalysis, [5] cancer applications, and as molecular contrast agents for dual efficient cancer diagnos- tics and selective photo-thermal therapy. Moreover, Au NPs were used in several biomedicine purposes such as leukemia therapy, [6] biomolecular immobilization, [7] as anti-angiogenesis, anti-malaria and anti-arthritic agents. [8] Surface–enhanced Raman Scattering (SERS) is a rapid, highly sensitive, reagent–free and non-destructive technique that has important implications in biological research in terms of analyzing the chemical composition within a single living cell at unprecedented resolution. [9] Recently, many studies have utilized colloidal suspension of metallic NPs mainly Au and silver (Ag) to monitor cellular processes and events that take place inside living cells. [10] The delivery of Au NPs inside human cells based on a passive uptake mechanism was recently reported; [11] however, this approach has several drawbacks, such as lack of control over aggregation, non–homogeneous distribution of NPs and a very poor translocation efficiency of NPs to the cell nucleus, which results in a relatively low reliability and reproducibility in the SERS analysis. The cell nucleus is the most important cell orga- nelle because it encompasses the genetic information that plays a critical role in most cell functions i.e. cell growth, prolifera- tion, and cell apoptosis. [12] Targeting the nucleus with NPs is a promising approach in biological research due to its role in different cell functions. However, nuclear targeting is difficult to achieve because the NPs must pass into the cytoplasm and then cross the nuclear membrane. [13] In addition, NP targeting of cancer cell nuclei has been reported to influence cellular function, causing cytoki- nesis arrest, DNA damage, and programmed cell death, which leads to failed cell division, thereby resulting in apoptosis. [14] Therefore, many studies have attempted to develop methods of forming metal NPs inside the human cell nucleus. Recently, certain microorganisms such as bacteria, fungus, yeast and actinomycetes were reported to have the ability to synthesize different metallic NPs from their ions. [15] Further- more, Anshup et al., [16] and Shamsaie et al., [17] reported the extracellular and intracellular syntheses of Au NPs based on the reduction of auric chloride. Here, we aimed to explore the potential of forming NPs (Au and Ag) intracellular and extracellular in different human living cell lines (cancer and healthy cells) through the reduction of ions. In addition, we examined effects of these metal ions (auric chloride or silver nitrate) on cell viability as well as cell morphology in different living cell lines. Our results demonstrated that treatment of different cell lines with metal ions resulted in the cell fixation. While, AFM, TEM, EDX, SEM and UV-Vis absorption techniques were demonstrated the formation of metal NPs inside the cell's nucleus as well as larger particles of different sizes and shapes in the incubation solution. In addition, the treated cells shown strong Raman signals compared with weak and noisy Raman Adv. Mater. 2014, 26, 910–918